Color television system

ABSTRACT

In a color television signal the total line length or period and the bandwidth requirement can be conventional, but the active line period is increased to e.g. about 94% of the line period, giving an aspect ratio of about 3:2 instead of 4:3.

BACKGROUND OF THE INVENTION

This invention relates to color television systems.

All existing broadcast television standards have a picture aspect ratio(the ratio of picture width to picture height) of 4:3. This ratio waschosen for compatibility with ordinary motion picture standards.

A greater sense of realism could be conveyed by television pictures ifthe aspect ratio were increased so that the picture filled more of theviewer's field of view. Wide-screen presentations are now commonplace incinemas. A number of proposals have been made for television standardswith a higher aspect ratio, but these all involve a higher videobandwidth.

This invention enables the provision of a higher aspect ratio within thesame bandwidth as existing television standards.

In the U.K. System I 625-line standard, the total length of the line is64 μs. However, only 52 μs is used for the picture. This is known as theactive line period. The remaining 12 μs, known as the horizontalblanking interval, is required to transmit a synchronising pulse for thehorizontal synchronising of the receiver, a black level pulse whichprovides a d.c. clamping reference, and a burst of color subcarrier tosynchronise the receiver's PAL decoding circuits. The receiver uses thetime of the horizontal blanking interval for horizontal flyback of thescanning spot in the cathode ray tube to the start of the next line.

SUMMARY OF THE INVENTION

The present invention is defined in the appended claims to whichreference should now be made.

In a system embodying this invention we propose that the total linelength of 64 μs is retained, but the active line length is increased.The remaining time would be used to provide horizontal synchronisinginformation and a period of black level as a d.c. clamping reference.

In this way it is possible to achieve an aspect ratio of greater than4:3. The active line may constitute at least 85% or even 90% of the lineperiod, and the color synchronising information may be transmittedeither during the black level pulse or during the vertical blankinginterval, so that there is no separate period of color synchronisinginformation during the line period. As a further alternative, colorsynchronising information could be obtained from the digital soundsignal or its carrier or multiplex system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail, by way of example, withreference to the drawings, in which:

FIG. 1 illustrates in diagrammatic form one television line according toexisting television standards;

FIG. 2 is a similar drawing of a first television line embodying thisinvention, using a narrow synchronising (sync.) pulse and a reducedcolor burst superposed on the black level portion of the signal;

FIG. 3 is a similar drawing of a second television line embodying thisinvention using a wider sync. pulse but with the color synchronisinginformation transmitted separately.

FIG. 4 is a schematic diagram showing how color synchronizinginformation may be transmitted with the sound signal;

FIG. 5 shows a 5 MHz bandwidth signal; and

FIG. 6 shows, schematically, transmission of a color burst in a line inthe vertical blanking interval.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The conventional television line shown in FIG. 1 has a line period of 64μs, of which 52 μs constitutes the active video signal, this being about81% of the line period. The remaining 12 μs is used as flyback time andfor synchronising information. More particularly, the line commenceswith a line sync. pulse and is then followed by a period of black leveltransmitted as a d.c. reference and on part of which is superposed thecolor synchronising burst. All this is well known.

In accordance with the embodiments shown in FIGS. 2 and 3, the activevideo signal occupies 60 μs or nearly 94% of the line period. This givesan aspect ratio increased from 4:3 or 1.333 to 1.538. Coloringinformation may be transmitted in the active video using the PAL systemsubstantially as at present. "NEW PAL" techniques may be used fordecoding the signal with a different form of color synchronising burst.

To carry color synchronising information, the embodiment of FIG. 2 usesa short burst which is transmitted superimposed on a reduced period ofblack level. The line sync. pulse is also shorter.

FIG. 3 shows an embodiment in which the color synchronising informationis not transmitted during the relevant line period at all. It may thenbe transmitted in various other ways. For example, a much longer burstof color subcarrier (which could extend over several lines) may betransmitted on unused lines during the vertical blanking interval of thesignal, as shown in FIG. 6, for example. Alternatively, the soundcarrier signal in the composite PAL signal could have a frequency whichwas simply related to the color subcarrier frequency, e.g. one and ahalf times the subcarrier frequency, which for PAL system I isapproximately 6.645 MHz. (Such sound carrier locking has been proposedfor two-channel sound systems for television, particularly for satellitebroadcasting). Other possibilities would be to obtain colorsynchronising information from the timing of digitally transmitted soundsignals or from `housekeeping` signals in a data multiplex system.

A schematic diagram showing the color synchronized signal beingtransmitted with the sound signal, for example, is depicted in FIG. 4.

The system of FIG. 3 would maintain line synchronisation better in thepresence of noise than the FIG. 2 embodiment.

A modified form of the PAL system may be used where chrominance, lowfrequency luminance and high frequency luminance are transmitted inthree separate frequency bands by frequency-shifting the high frequencyluminance to above the chrominance frequency band.

The system could be particularly beneficial when storage andinterpolation are used in the receiver to increase the display line andfield rate, reducing visibility of the television line structure andeliminating flicker, as described in our British Patent Application2,050,109. The higher aspect ratio given by a system embodying thisinvention, in addition to the above improvements, would give a displayof higher quality than is achieved with present receivers and thepresent broadcast system, but without increasing the bandwidth requiredfor transmission. Thus although the increased aspect ratio requires somedeparture from compatibility, existing transmission channels could beused and the modifications at the receiver represent a relatively minorchange, comparable with those required for limited access services.

The system would have particular utility with receivers using matrixaddressed displays such as may become available in the future. Suchreceivers would not require flyback time as at present. Techniques forextracting timing information are now such that the well-definedhorizontal synchronising pulse and colour synchronising burst currentlyemployed are no longer required to the same degree of definition.Several proposals for limited-access television services using differentforms of synchronisation have been made, and a practical implementationof the invention can be based upon such a system with appropriatealteration to the system timing.

Thus the circuitry required for implementation of the present inventionis identical to that required for conventional television signalprocessing, the only alterations necessary for the FIG. 2 embodimentbeing to retime the duration of the various components of the signal. Inthe FIG. 3 embodiment the retiming would extend to transmitting thecolor synchronising information outside the line period or as notedabove, in a separate part of the composite signal.

The proposed system would not be compatible with existing receiversbecause of the shortening or removal of the normal line synchronisingpulses.

It should be noted that in the present U.K. PAL System I the active lineperiod of 64 μs is divided as to 811/4% active line period and 183/4%blanking period having an exemplary 5 MHz bandwidth as shown in FIG. 5.It is proposed in accordance with this invention to provide an activeline period which is greater than 85% and preferably greater than 90%and 95% up to a maximum in the region of 971/2%. This leaves up to onlyabout 1.6 μs for the horizontal blanking interval. The aspect ratiocould be increased from the present 4:3 or 1.333:1 to up to 4.8:3 or1.6:1, though the value of 3:2 or 1.5:1 represents a useful increase.

The video bandwidth requirements are in this way not increased overthose currently pertaining.

We claim:
 1. In a standard color television system using a color videoinformation signal having a standard line duration and comprising anactive video information portion and a non-active video informationportion, said system further having defined bandwidth requirements and adefined relationship between the picture aspect ratio thereof and theactive video information portion for a given picture height, theimprovement comprising a color television video signal for use in saidsystem wherein the active video information portion occupies at least85% of said standard line duration, whereby the picture aspect ratio isincreased to a ratio greater than a 4:3 ratio without increasing saiddefined bandwidth requirements and without substantially changing saiddefined relationship.
 2. A color television signal according to claim 1and further wherein color synchronizing information is transmitted inanother signal which is separate from said color television videosignal.
 3. A color television signal according to claim 2, in which saidother signal is an audio signal for use in said system.
 4. A colortelevision system according to claim 5, in which color synchronisinginformation is transmitted during the vertical blanking interval.
 5. Acolor television signal according to claim 1, in which a d.c. clampingreference is transmitted during the non-active-video information portionthereof.
 6. A color television signal according to claim 1 wherein saidactive video portion is greater than 90% of the total line duration. 7.A color television signal according to claim 1 wherein said standardline duration is about 64 microseconds and said defined bandwidth isabout 5 MHz.